Hyperthermia for cancer therapy will be generated in tissues using prototype 915 MHz microwave applicators. New applicators will be designed and fabricated at lower frequencies for better tissue penetration. A temperature profile control system will be developed and evaluated using surface cooling and microwave power control loops. In situ temperature measurement will be made by nonperturbing GaAs semiconductor fiberoptic probes. Demonstration tests of the hyperthermia system will be performed in animals to demonstrate its therapeutic potential.